Decoding the Principles Governing Molecular Cage Precipitation of Aliphatic and Perfluoroalkyl Acids (PFAAs)

Perfluoroalkyl acids (PFAAs) are surfactants that rank among the most persistent and hazardous anthropogenic pollutants. Molecular cages have emerged as promising remediation agents, enabling the straightforward isolation and purification of PFAAs through selective binding and precipitation. However, critical gaps remain regarding (i) the degree of genuine selectivity for PFAAs over structurally analogous aliphatic surfactants, (ii) the structural features that govern cage-surfactant precipitation, and (iii) cage performance in mixed-surfactant systems. The absence of systematic investigations has impeded the rational design of cages with targeted selectivity and a limited understanding of their behavior in chemically complex environments. Herein, using one of the most efficient cages reported for PFAA removal, we address these questions and demonstrate that molecular cages do not intrinsically discriminate between fluorinated and aliphatic surfactants; instead, lipophilicity is the primary parameter controlling precipitation. Moreover, we show that surfactants in mixtures can be selectively isolated in an ordered fashion according to their lipophilicity.